The present invention relates to a high-alloyed, passivatible, austenitic-ferritic steel alloy and to a method of making and using pipes or receptacles from blanks or billets made of such an alloy.
High-alloyed steel is used for pipes, tubes, and equipment that conduct, hold, process, and otherwise transport and handle acidic gases, such as natural gas. An alloy of this type is described, for example, in German printed patent application No. 26,16,599. This alloy has the following consistency (all percentages by weight):
0.001 to 0.12% carbon PA1 0.2 to 1.5% silicon PA1 0.5 to 8.0% manganese PA1 12.0 to 30.0% chromium PA1 2.0 to 16.0% nickel PA1 0.1 to 5.0% molybdenum PA1 0.01 to 1.2% titanium PA1 0.01 to 1.6% niobium PA1 0.01 to 3.5% copper PA1 0.01 to 0.35% nitrogen PA1 up to 0.05% carbon PA1 20% to 25% nickel PA1 5.0 to 9.5% nickel PA1 3.0 to 6.0% molybdenum PA1 0.01 to 2.5% copper PA1 0.1 to 1.5% silicon PA1 0.5 to 2.5% manganese PA1 0.05 to 0.3% nitrogen
The remainder being iron and the usual metalloids.
This known steel is, indeed, satisfactory with respect to resistence to corrosion from hydrogen sulfide and carbon dioxide as well as chlorides, provided these components contained in natural gas do not exceed rather critical limits. This known alloy is also strong and can be welded. However, ductability and toughness, particularly at low temperatures (e.g., -70.degree. C.) is not satisfactory.